Cylindrical array antenna system with electronic scanning



Oct. 21, 1969 N. SHESTAG ET AL 3,474,446

CYLINDRICAL ARRAY ANTENNA SYSTEM WITH ELECTRONIC SCANNING Filed Feb. 26, 1968 a Sheets-Sheet 1 .Fza J.

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AGlfA/T Oct. 21. 1969 L. N. SHESTAG ET AL 3,474,446

CYLINDRICAL ARRAY ANTENNA SYSTEM WITH ELECTRONIC SCANNING Filed Feb. 26, 1968 8 Sheets-Sheet 2 4 INVENTORS. LOWEZL NOE/MAN f/(fSMG 77-QM/45 K/A/AGA 04.21, 1969 4. SHESTAG ET AL 3,474,446

CYLINDRICAL ARRAY ANTENNA SYSTEM WITH ELECTRONIC SCANNING Filed Feb. 26, 1968 8 Sheets-Sheet I3 T. 1 M50 B 9 :54:

INVENTORS. LOWELL A/oemA/sywme 7/40/1445 LVN/46A AGE/VT Oct. 21, 1969 L, s s ET AL 3,474,446

CYLINDRICAL ARRAY ANTENNA SYSTEM WITH ELECTRONIC SCANNING Filed Feb. 26, 1968 a Sheets-Sheet e.

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INVENTORQ. mmfa NOE/HAW 67/657216 F g/14 45 K/A/AGA AGf/VT United States Patent O 3,474,446 CYLINDRICAL ARRAY ANTENNA SYSTEM WITH ELECTRONIC SCANNING Lowell Norman Shestag, Palos Verdes Peninsula, and Thomas Kinaga, Palos Verdes Estates, Calif assignors to International Telephone and Telegraph Corporation, New York, N.Y., a corporation of Delaware Filed Feb. 26, 1968, Ser. No. 798,151 Int. Cl. H04h 7/02 U.S. Cl. 343-100 10 Claims ABSTRACT OF THE DISCLOSURE A system is shown for producing a continuously rotating (scanning) radiation pattern from a cylindrical array antenna. The complete antenna comprises columnar vertical arrays each disposed parallel to the cylindrical axis, each M elements high, and N such columns disposed about the circumference of the cylinder. Assuming that the cyclinder axis is the vertical, the elevation plane radiation pattern is formed by the characteristics of each column with its M radiating elements driven in accordance with the desired shape. The azimuth radiation pattern is produced by field summation of the individual columnar array energies.

The individual column excitations are amplitude modulated and no microwave phase modulation techniques are required. Although the 'basic configuration is adapted to radiation of arbitrary patterns in both planes and arbitrary scan programming in azimuth, the described embodiment radiates an omni-directional multilobed pattern which is caused to rotate in azimuth :by selection of the modulation functions of each column of radiators. Microwave amplitude modulators for each column of radiators are controlled in accordance with summed first and second low frequencies. Such low frequencies are harmonically related and staggered in phase as applied at each successive column about the cylinder circumference so that the field which produces the azimuth pattern rotates, resulting in a rotating (scanning) gearshaped azimuth pattern.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to antenna systems for radiation of electromagnetic energy and more particularly to antenna array systems with arbitrarily predetermined pattern characteristics and capable of inertialess scanning in at least one angular space coordinate.

Description of the prior art In the prior art there have been a number of systems for radiating patterns similar to those of which the present invention is capable. The particular system instrumentation described herein which utilizes the present invention was developed to radiate the rotating gear shape pattern required by the so-called TACAN, a navigational guidance system. This system is described in detail in chapter 12 of Electronic Aviation Engineering" by Peter C. Sandretto, a reference handbook published in 195 8 by International Telephone and Telegraph Corporation, New York. In that reference, a typical prior art antenna system for the TACAN ground transmitter is described. In that instrumentation as well as in some other prior art techniques for scanning the radiation pattern from a cylindrical array, mechanical means are used to obtain the desired pattern rotation (scanning).

In general, such prior art mechanical devices fall into three categories. The first of these is physical rotation of part of, or an entire antenna assembly. Next, there is the commutating feed type of system, and finally there is the goniometer approach. In addition, there are apparently several non-mechanical techniques. In general, these may be categorized as electronic switch commutating of elements or combinations of elements, phase shifting exciters for varying the antenna aperture energy distribution and therefore resulting beam angles, and differential amplitude control of element excitation. In the latter technique, individual controlled, radio frequency amplification at each array element, or for groups of elements, has been proposed.

In the case of all mechanically scanned antennas, there is the obvious limitation imposed by inertia and weight of mechanical elements, and in addition the disadvantage of fixed beam shape such that variation of beam shape as a function of scan angle is impossible or at least very difiicult and cumbersome. Sector scanning is diflicult and not practically possible at rates in excess of about 200 Hz. Mechanically commutated systems are impractical at microwave frequencies because of coupling and radiation problems. Goniometer type scanners, both mechanical and electrical, are limited to arrays with four times as many radiating elements as the highest fourier component in the mathematical function which describes the polar pattern. This presents a severe design restriction, since there can be many reasons requiring the employment of another number of elements.

An important limitation imposed on electronic switching or commutating results from the fact that such systems allow beam movement only in discrete steps. Moreover, beam scanning by means of plural controlled amplifiers is impractical at microwave frequencies whenever high reliability is required, since active elements are necessary and these inherently limit reliability. Cost factors are also strongly against the plural controlled amplifier concept.

Inertialess and continuous scanning can, of course, be effected through use of electronic phase shifting of the array element excitations, however, practical devices for this instrumentation exhibit very non-linear behavior and require high levels of modulating power. The use of :discrete step phase shifters results in similar problems as noted in connection with switching or commutating feeds (i.e., angular scanning resolution is relatively coarse and beam shape is not readily controllable).

SUMMARY OF THE INVENTION Electronic scanning of an array by means of the technique of the present invention eliminates or substantially ameliorates all of the problems associated with the aforementioned prior art devices. It also allows certain aspects of antenna design to be accomplished, which cannot be fully realized by prior art devices.

The most evident advantage of the present invention is the elimination of the problems of mechanical scanning, such as weight, drive power, cost, maintenance and susceptibility to environmental extremes. It allows elimination of the scan speed limitation and permits sector scanning to be readily accomplished.

Using an array designed for a particular application with electronic scanning in accordance with the present invention, either continuous or discrete step scanning can be effected. The characteristics of the array in the nonscanning coordinate can moreover, be made to fit any arbitrary beam shape function as a function of angle of scan. Thus, if scanning is eifected in the azimuth plane, the vertical beam shape may be tailored to fit a predetermined plan simply by design of the vertically disposed element combinations or through use of auxiliary deflectors at predetermined angular positions. Modification of the phase distribution of energy feeding the vertically disposed element stacks can also produce variation in elevation beam shape over portions of the azimuth coverage. It will be apparent when the detailed instrumentation described is understood that azimuth beam shape may also be a controllable parameter throughout the scanning angles of interest.

An outstanding feature of the technique of the present invention is that it allows optimum design of a cylindrical array. Thus any number of radiating elements can be used in an azimuth ring of elements. The criterion to be met is the number of elements (elements per increment of azimuth angle) required for the required azimuth pattern shape.

A goniometer system, for instance, is restricted to a number of elements, not exceeding four times the highest Fourier Component in the mathematical pattern function. This limitation may well preclude the development of a proper azimuth pattern shape. Achievement of an optimum number of elements in a mechanically scanned antenna system is frequently precluded by size, weight, and the resulting inertial problem. Moreover, most prior art cylindrical arrays utilize lural concentric ring arrays, resulting in lack of coincidence among the pattern modulation components.

The employment of the technique of the present invention allows essentially complete design freedom so that antenna characteristics can be freely optimized in the light of the entire antenna performance requirement.

The technique of the present invention requires the use of only passive (preferably solid-state) non-mechanical components, a fact which maximizes its inherent reliability. Moreover, the unique combination of elements and sub-arrays facilitates routine maintenance while in operation. Individual component failures do not produce total failure in contrast to the situation prevalent in connection with prior art systems. Unattended operation over extended periods is therefore possible, a fact of great importance in connection with the TACAN or other navigational systems.

Microwave phase modulation, a necessary part of many prior art electronic scanning systems, is not required by the system of the present invention.

More easily obtained, more precise and more linear amplitude modulation is utilized instead of the more difiicult, less flexible phase modulation.

A cylidnrical array of microwave radiating elements is employed since the illustrated embodiment of the present invention is intended to produce a pattern which scans at full 360 in the azimuth plane.

Given a desired far field pattern, the required aperture energy distribution may be determined by classical methods. In the present instrumentation, the principal concern is with beam shape and scanning (in the azimuth plane since the array axis is assumed to be vertical) of the pattern desired. Most radiation patterns of interest in the a plication of the technique of the present invention are capable of being represented by a series of cos terms, at least by approximation.

The variation of aperture excitation circumferentially as a function of azimuth angle for the gear shaped 9-tooth pattern desired is describable in accordance with the following:

Equation I In Equation 1 the first and ninth cosine terms are used; It is the array element number and N is the total number of elements around the array. The constant C and D, which proportion the first and ninth cosin terms, will be discussed in the detailed description later in this specification.

In order to effect rotation (scanning) of the pattern, the excitation is caused to revolve around the antenna. Mathematically, this is accomplished by introducing a time factor into Equation I giving rise to the following:

D cos 9[(n1)- Qt] Equation II In Equation II, Q is the rotation (scanning) rate in units compatible with it. Physically is the relative phase of the modulation at element It, and there are N polyphase signals at each modulation frequency. The general expression for the element (each column of commonly fed radiators constituting an element in this sense) modulation is given as follows:

Equation III In Equation III, values of K are chosen in accordance with particular system application requirements.

The oscillation of the excitation at each element is such that the excitation pattern appears to rotate around the antenna circumferentially, with the result that the radiation pattern appears to rotate around the antenna at the same rate. From another point of view, the variation of the excitation on the antenna results in a wave travelling around the antenna. The far field radiation pattern caused by this wave then may be said to rotate with it.

In the present invention each circumferential element (column of radiators) is fed individually in accordance with Equation III with a discrete value of N for each of said elements. The result is a predetermined fixed, progressive phase displacement between adjacent elements around the array. The effect of a rotating field and resultant radiation pattern may be likened to the rotating magnetic field concept in connection with polyphase electric motors. The vector addition of energy components which produces the far field pattern is accomplished entirely as a result of amplitude modulation of element energization and Without any requirement for phase modulation. The technique is adapted to either pulse or C transmissions and is reciprocal (i.e., may receive as well as transmit).

Electronic circuits provide the necessary first and ninth order periodic waves and combine these for generation of the modulation functions with appropriate phase shifting applicable to each circumferential radiating element. The amplitude modulation of microwave energy for each element is accomplished as a function of and in response to the corresponding modulation function by a PIN diode modulator. The latter device is an efficient and reliable component for that use.

It may be said that the general object of the present invention is the development of an electronic scanning or beam positioning antenna system which is reliable, rugged and accurate. As a part of the object, flexibility in respect to beam shape and adaptability to selection of an optimum number of radiating elements were also sought. Other objects and advantages will be apparent from the prior art discussion and the detailed description to follow.

BRIEF DESCRIPTION OF THE DRAWINGS For the purpose of illustration and description, drawings are provided as follows:

FIGURE 1 is a pictorial drawing of a cylindrical array (with coordinate identification) for use in the system of the present invention.

FIGURE 2 is a partial exploded view of the array of FIGURE 1 illustrating the modular construction.

FIGURE 3 is a drawing of one element (vertical column of radiators) with associated power divider, modulator and modulation function generator.

FIGURE 4 is a functional block diagram of the components for modulation function generation.

FIGURE 5 is a detailed circuit of a single frequency quadrature phase signal generator.

FIGURE 6 is a detailed circuit of a typical modulator driver amplifier circuit.

FIGURES 7A and 7B are graphs of the modulation function for an arbitrary first and eleventh antenna elment, respectively.

FIGURE 8 is a polar plot of a typical azimuth excitation function (aperture distribution diagram).

FIGURE 9 is a typical far field radiation pattern corresponding to the excitation function of FIGURE 8.

DETAILED DESCRIPTION The particular instrumentation of the present invention herein described, and the antenna pattern developed is particularly adapted to air navigation ground systems, specifically the previously referred to TACAN system.

Before introducing the details of the system configuration and instrumentation, it is considered desirable to discuss the general problem in broad theoretical terms.

The general requirements for the TACAN radiation fields will be examined first without regard for any specific antenna configuration which may be required to generate these fields. In this way, broad guidelines for the detailed discussion can be established.

The function of the radiation pattern is to generate a time varying voltage in an aircraft receiver of the form:

for all values of as over a range of elevation angles 0 between 0 and 50 Where w =angular field rotation rate, (15 c.p.s. in the embodiment descriped), M and M =coefficients determining modulation levels, and =azimuth angle from an arbitrary directional reference. The space geometry is shown in FIGURE 1, where the indices in and n indicate column and ring element numbering. The modulation coefiicients, M and M fall in the range 0.10 to 0.30 for satisfactory operation.

It is normally desirable to provide constant coverage versus range for a given altitude; a result closely approximated in practice by requiring the elevation pattern above the beam peak to be proportional to cscfi. Furthermore, the elevation sidelobe structure on the ground side of the beam should be kept as low as possible (in the -20 db region) to reduce multipath site effects which can deteriorate the radiation pattern. The roll-off of the main beam is required to be such that the slope at the horizon should be at least 0.07 volt per degree on the ground side to reduce ground effects While assuring low altitude coverage. In practice, the main beam is also pointed slightly above the horizon to provide maximum relief from sitting problems.

If it were possible to generate precisely the radiation pattern described in Equation V, the system accuracy would be limited only by the receiver and reference pulse characteristics. However, errors in the lobe structure are certain to occur due to various design approximations, the geometry of the antenna, manufacturing tolerances, sitting errors, etc. These errors will cause F -(,t) to take on the form:

Equation V where the desired terms are M M and Other terms (M are unwanted harmonics of the fundamental modulation rate, and their very presence indicates that a finite A 5 (error) term has been generated. In the particular antenna design, the acceptable level of these extraneous harmonics was limited to 20 percent.

It is evident that the function F (,t) is the signal which the aircraft receiver actually measures and, as such, is the most appropriate yardstick for determining antenna performance.

Inspection of Equation IV shows that if either w t or a5 is varied through one complete period, while the other remains constant, exactly the same function is traced. Thus, the same contour is measured if the amplitude is plotted along a constant radius path extending 360 degrees around the antenna in a horizontal plane as that obtained by remaining at point P and allowing the pattern to be rotated once. This is a very important feature of a practical TACAN pattern. In fact, since an aircrafts position cannot change significantly during many cycles of the comparatively rapid pattern revolution, the modulation as a function of time at a point in space should be studied rather than the antennas static radiation pattern. Evaluation of antenna performance for design purposes is most easily handled if the Equation V is rewritten as:

Equation VI where M =2[a +b 1/2 and Equation VI is a Fourier series. Therefore, when the azimuth radiation pattern of the antenna is computed or measured, it can be readily analyzed to determine hearing error, 11%, and harmonic content, M,, 1,9). This is exactly what was done during the original study of antenna design per se. A computer can perform this analysis as the second step of a program that calculates the radiation pattern, and variation of antenna physical constants progressively modified and reevaluated until satisfactory performance of the cylindrical array is indicated.

Referring now to FIGURE 1, a pictorial representation of a cylindrical array suitable for use in the system of the present invention is shown. The antenna radiation elements, of which 103, 104, 105, and 106 are typical, are distributed in rows and columns circumferentially about the cylindrical array which is pictured with its axis disposed generally vertically. Each of these radiators may be called a slot backed by a cavity and excited by a probe connected to a coaxial feed line, in a manner well known in the art. The said radiating elements are arranged in columns each M elements high with N elements on the circumference. Thus there are N of the M element vertical columns about the circumference of the arrray. An end bell structure, top and bottom, is represented at 101 and an array cover or radome 102, which would normally protect the array from environmental hazards, is shown partially cut away to facilitate an understanding of the element arrangement.

In a particular column, elements 103 and 104, for example, begin from the bottom and corresponding elements 105 and 106 in the next adjacent column are slightly staggered vertically so that a desired circumferential spacing may be attained through the resulting interleaving of elements in adjacent columns.

In FIGURE 1, the (small) letter m, represents the ordinal number of an arbitrary one of the in individual radiators in a column or the mth row from the bottom. The (small) n position represents the ordinal number, from an arbitrary peripherical point, of the n radiators around the circumference.

In describing the system of the present invention, an element in an overall sense will mean a column of radiators, since these will be seen to be fed, in common (in phase) i.e., each column as a unit. The angle will be seen to describe the elevation angle of radiation and is used to represent the azimuth angle. Thus an arbitrary point as depicted with respect to the FIGURE 1 array in three dimensional spherical coordinates is P(r,0,) where 0 and are as described and r is range.

Looking ahead momentarily to FIGURES 8 and 9, a particular aperture energy distribution and resulting desired far-field antenna radiation pattern are respectively depicted.

Although, as already indicated, the system of the present invention is adapted to the generation of most arbitrary azimuth radiation patterns, in the particular embodiment illustrated and herein described, a gear shape omnidirectional pattern was required and the detailed instrumentation was constructed accordingly.

Referring now to FIGURE 2, a support structure and a module of radiators is shown in exploded form. The end bells 101 are shown joined by structural rod members 201 (typical) in a very straightforward mechanical configuration. The radiators 103 through 106 are shown in positions corresponding to FIGURE 1. These and all other radiators in the module are flush mounted at their openings on a curved planar skin 209 which interleaves with the corresponding surfaces on the adjacent modular assemblies. Eleven such subassemblies of 32 radiators were required to complete the cylindrical array in a typical embodiment requiring 44 columns each 8 elements high (producing 16 horizontal rings in view of the vertical staggering of radiators illustrated in FIGURES 1 and 2).

The radiators in each column are fed from column feeds partially visible in FIGURE 2 at 204, 205, 206, and 207. The radiators in the column including radiators 105 and 106 are fed from 204 and those radiators in the column including radiator 103 are fed from 205. Similarly, 206 and 207 are the (energy distributors) feeds for columns containing 210 and 211 respectively. The actual radiators are open waveguide sections (cavity backed slots) typically 203 and 208. These sections are depicted in more detail in FIGURE 3 and will be further described in connection with that figure. The Wedge shape piece 202 which appears in each cavity is a ridge included to produce the effect of a ridge loaded waveguide section. This expedient is one of a number of suitable matching techniques available for slot radiator schemes such as illustrated.

Referring now to FIGURE 3, a single column of radiators is depicted, corresponding to the column containing cavity backed slot radiators 105, 106 and 203 in FIG- URES 1 and 2, and without the surface plate 209.

A column feed 204 feeds the eight radiators illustrated through coaxial connections (typically 311 feeding 203) respective probes within each cavity in a manner well understood by those skilled in the related art. The distribution of energy from 204 to the radiators influences the characteristics of the beam in elevation, a subject which will be further discussed later in this specification. N of these column feeds are required corresponding to N columns of radiators.

Element 309 (N required) is an amplitude modulator which directly provides the radio frequency energy distributed by 204. An RF connection between 309 and 204 may be appropriately effected through a coaxial coupling or any other known RF coupling technique similar to 311.

A very satisfactory device for performing the function of the modulator 300 is the so-called PIN Diode Modulator. Its theory and construction are known and are described in the technical literature. One such description appears under the title Microwave Variable Attennation and Modulators Using PIN Diodes by I. H. Hunton and A. G. Ryals in the IRE (now IEEE) Transactions PGMTT, vol. MIT- (July 1962, pp. 262-273.

The RF line (coaxial cable or other suitable transmission line) 306 conveys unmodulated RF from transmitter (or radio frequency generating means) 313 to the modulator 309 through power distribution network (power divider) 301. The device 301 is similarly known in the art. Its function is to divide power supplied such as from a transmitter into an input transmission line 312 substantially equally among the N output ports. In addition to the output taken at 306, ports 307 and 308 are also typical and apply to other adjacent modulator, column feed and column of radiator combinations.

Each modulator 309 also accepts a discrete modulator control signal on a cable 303. Said control signals are produced by electronic control circuitry represented by 302.

Other modulators in the system are controlled by discrete signals on corresponding outputs of 302, such as outputs 304 and 305. Further details relating to these circuits will be given as this description proceeds.

Referring now to FIGURE 4, the components contained in the 302 block are depicted in more detail. In the particular embodiment described, the antenna pattern has nine lobes and a basic rotation rate of 15 revolutions per second.

The basic modulator control signal frequency is 15 Hz. with a Hz. (9th harmonic) content, and the resulting nine rotating lobes thus occur at forty degree intervals (see FIGURES 8 and 9).

Returning to FIGURE 4, it will be noted that a 135 Hz. tuning fork controlled oscillator at 401 provides the basic modulation control timing. The fundamental 15 Hz. azimuth scan control signal is generated by a phase locked oscillator 403. A fraction of the 401 signal is supplied on lead 402 to effect this synchronization.

The 135 Hz. signal from 401 is supplied on lead 404 (in inverted form) to a quadrature phase generator 405 which has outputs 412 through 415 at four discrete phase positions corresponding to O, 1r/2, 1r and 31r/2 positions. Similarly the zero phase 15 Hz. signal on lead 406 drives a 15 Hz. quadrature phase generator 407 to produce 0, 1r/2, 1r, and 31r/2 outputs through 411. The details of construction of the quadrature phase generators 405 and 407 are illustrated in FIGURE 5 and will be discussed in connection with that figure.

The blocks 4'16, 417 and 418 each comprise a composite signal forming network for mixing the desired balance of 15 Hz. and 135 Hz. components (in accordance with selected values of M, and M in Equation IV) and a driver amplifier for providing an adequate modulator driving signal power level. Given the four phase vectors for each Fourier component (the 15 Hz. and 135 Hz. components), each of the blocks 416, 417 and 418 is capable of supplying its corresponding modulator with a varying signal in any relative phase relationship by means of two selected vectors it receives at each Foutiee frequency. It will be noted that 416, 417 and 418, (the modulator mixer-driver circuits) are each shown connected to an arbitrarily selected pair of the aforementioned four phase vectors. An additional phase shift for precisely placing the vector of each modulator control signal at the predetermined phase position desired i provided within each of the blocks (of which 416, 417, an 418 are typical). There are m modu lator mixer driver circuits required, just as there are 11 columns radiators and n modulators.

Since the quadrature phase signals from 405 and 407 represent the full range of modulation signal phases corresponding to a full 360 of scan, it is possible to choose any given phase position and relate this to a discrete bearing angle. Although not specifically a necessary part of the present invention, the reference index trigger generator for use with the TACAN equipment is illustrated at 420. By turning a shaft 419, it is possible in a device such as 420, to control a resolver, sine/ cosine potentiometer or similar device to select a phase (bearing) and generate a marker pulse at one or more angles as the scan passes these angles. Leads 421 and 422 carry such information in pulse or trigger form for a pair of such angles. A means of conveying the pattern scan information is always necessary.

Referring now to FIGURE 5, it will be noted that this typical quadrature phase generator is applicable at both 405 and 407. The input would thus be from lead 404 or 406 and the four phase outputs are 408 through 411 or 412 through 415, as appropriate.

Operational amplifiers 501 (non-inverting) and 502 (inverting) are connected in a conventional circuit arrangement to accept the 404 (or 406) input. A phase shift bridge, comprising capacitor 503 with fixed and variable series resistance 505 and 506 respectively, and capacitor 504 with fixed and variable series resistances 507 and 508 respectively, is driven between the 501 and 502 outputs: The bridge midpoints feed leads 509 and 510 to produce the 1r/2 and 31r/2 vectors while the bridge drive pair 511 and 512 thereby become the zero and 1r vectors respective ly. The leads 509, 510, 511 and 512 then become the inputs for operational amplifiers 513, 514, 515 and 516, respectively. The outputs of these later amplifiers are then the aforementioned four vectors as indicated on FIG- URE 5.

Referring now to FIGURE 6, the typical instrumentation for the modulator mixer-driver circuits will be described.

The circuit of FIGURE 6 is typical of 416, 417, and 418 as illustrated in FIGURE 4. The total requirement for duplication of this circuit is N, i.e., one such circuit for each modulator. The said modulator is illustrated (for reference) at 601.

For convenience of description, block 416 is selected as the arbitrary unit of FIGURE 6 circuitry to be described. The 15 Hz. and 135 Hz. inputs are correspondingly those shown on FIGURE 4, i.e., 408, 409, 412 and 413.

For the 15 Hz. signal, resistors 602 and 611 form an additive mixer which develops a signal at point 606 which is the vector sum of that at 408 and the tap of variable resistance 604. If, for example, the values of 602 and 611 were equal and the applied signal voltages were equal, the signal at 606 would have a phase at the 45 point between the and 1r/2 inputs. Other values of the mixer resistors and another setting of the 604 tap would produce a signal of another discrete phase position between the said 0 and 1r/2 inputs. Thus, the actual phase of the modulator signal appropriate to the circumferential antenna position and having the desired basic frequency of azimuth scan, is obtained.

The resistances 603 and 605 serve to predetermine the range of phase adjustment provided by 604 and to afford suitable vernier action in 604.

Also contributing to the composite signal at 606 is the 135 Hz. adjusted-phase signal through 607 and 612 acting together (and with whatever net parallel impedances apply at 606) to superimpose the correct amplitude 135 Hz. component on the 15 Hz. signal at 606. In respect to the 1r/2 input at 412, fixed resistances 608 and 610 and variable resistance 609 function in the same manner as recited in respect to 603, 605 and 604, respectively.

The composite signal developed across resistance 614 provides the input for the operational amplifier 619. This amplifier provides a signal level and source impedance appropriate to drive modulator 601 through a limiting resistance 618. Feedback resistance 615 functions with 619 in a well known manner and bias adjustment 617 has the effect of providing a DC level appropriate to the modulator operation.

All component parameters and signal amplitudes are determined in accordance with well known techniques once the specific system performance and driving requirements of the particular PIN diode modulator are determined.

Referring now to FIGURES 7A and 7B, two typical modulation functions as might be observed at the input to modulator 601 are shown. If the waveform of FIGURE 7A is assumed to represent the first circumferential element, then FIGURE 7B represents the 11th such radiating element. FIGURES 7A and 7B are otherwise self descriptive in the light of previous functional description of the system.

FIGURE 8, the antenna aperture illumination function in polar form at an instant of time, may be said to be the direct result of the appropriate FIGURE 7A and 7B excitations for all of the columns of radiations about the array circumference.

FIGURE 9 follows from FIGURE 8 based on the known expectation of the far field pattern resulting from the FIGURE 8 excitation. The reader is reminded that the rotation of the pattern is analogous to the rotation of the net field vector in a polyphase electric motor,

From an understanding of the principles of the present invention, modifications and variations will suggest themselves to those skilled in the art. For example, the vertical pattern of the columns of radiators may be entirely different. The feed of the vertical columns may be varied from column to column and the vertical pattern therefore varying about the circumference. Vertical patterns having nulls or other characteristices may also be included through appropriate column feeding arrangements or inclusion of reflectors at appropriate positions.

Azimuth patterns may be virtually any that can be represented or approximated by a series of cosine terms.

Vertical plane scanning over all or part of the azimuth coverage is also possible since the columns of elements will be realized to be frequency sensitive in that the vertical beam angle would be a function of frequency. This phenomenon and additional instrumentation for that effect are described in the copending U.S. patent application of J. F. Fling, S, L. Howard and F. M. Weil entitled Pencil Beam Frequency/Phase Scanning System, Ser. No. 570,991 filed Aug. 8, 1966.

Moreover, the system is entirely adaptable to receiving as well as transmission, and used as such (with receiver components replacing the transmitter) makes an efiective passive direction finder. In that mode, the modulation process is functionally the same as hereinbefore described.

What is claimed is:

1. An antenna and scanning system for radiating and rotating an arbitrary radiation pattern, said pattern being representable in a plane by a series of cosine terms, comprising: an antenna array including a plurality of radiating elements arranged in rows and columns, said array having a curved aperture at least along said rows whereby the direction of the array normal changes progressively along said rows; source means for energizing said columns of radiating elements each independently; a plurality of modulating means connected between said source means and said columns, each of said modulating means being connected exclusively to a corresponding one of said columns; and modulator driving means connected to each of said modulating means to control the amplitude of energy into each of said columns in accordance with a predetermined function, thereby to generate said arbitrary pattern in the far field of said antenna array by summation of the field contributions of said columns.

2. The invention set forth in claim 1 further defined in that said modulator driving means includes; a first quadrature phase generator for producing a plurality of substantially sinusoidal first signals separated from each other in phase by predetermined phase angles, said first signals being at the lowest of the frequency components in said series of cosine terms; at least one additional quadrature phase generator for producing a corresponding plurality of substantially sinusoidal second signals separated from each other in phase by predetermined phase angles, said second signals being at a predetermined harmonic of the frequency of said first signals; means for maintaining a predetermined phase relationship between said first and second signals; a plurality of mixing means each responsive to a predetermined phase adjacent pair of said first signals and a predetermined phase adjacent pair of said second signals for generating plurality of signal composite signals of discreate phase each for controlling a corresponding one of said modulating means.

3. The invention set forth in claim 2 wherein additional means are included for providing said first signals in the form of four independent signals at 1r/2 radians spacing in phase at said lowest frequency component, each on a separate output from said first quadrature phase generator, and for providing said second signals in the form of four independent signals at 1r/2 radian spacing in phase at said harmonic frequency from said additional quadrature phase generator.

4. The invention set forth in claim 3 wherein said mixing means includes means for determining the phase measured at said lowest frequency of said composite signals by vector addition of the corresponding adjacent pair of first and second signals in controlled proportions thereby to generate each of said composite signals at a discrete predetermined phase position between the phase limits represented by said corresponding adjacent pair of said first signals.

5. An antenna and electronic scanning system for radiating and rotating an arbitrary pattern in azimuth and elevation planes, said pattern in the azimuth plane being representable, at least by approximation, by a series of Fourier cosine terms, comprising the combination of: an antenna array including a plurality of columns of radiators arranged in a curved plane convex in the azimuth projection; a source of radio frequency energy; column feed means for feeding each of said columns from said source discretely in a manner so as to predetermine the elevation plane beam shape corresponding thereto; additional means for varying the amplitude of energization of each of said column feeds as a function of a basic scan rate, said additional means also including means for varying the phase of the variation of said energization of each of said columns progressively, each by a predetermined amount of phase shift with respect to the adjacent columns, thereby to generate said arbitrary pattern in said azimuth plane and cause it to rotate at said basic scan rate.

6. The invention set forth in claim 5 further defined in that means are included for predetermining the feed line electrical length between successiv radiators within each of said columns of radiators to predetermine the relative phase of radio frequency energy at each element within each of said columns, thereby to produce a vertical beam pattern which is an arbitrary predetermined function of azimuth angle.

7. An inertialess antenna and scanning system comprising the combination of: a cylindrical array with its cylinder axis oriented substantially vertically including a plurality of radiating elements arranged in columns distributed in juxtaposition around at least a portion of the circumference of said cylinder, said columns each being arranged to be individually excited with radio frequency excitation; a plurality of modulators, one for each of said columns, connected to modulate said excitation to each of said columns, said modulators each being responsive to a modulation control signal; means for generating a plurality of said modulation control signals, one such control signal for each of said modulators, said control signals comprising the Fourier frequency components of the desired pattern, each of said modulation control signals having a predetermined phase shift with respect to the modulation control signals corresponding to the adjacent columns, such that said columns are supplied with varying radio frequency excitation thereby to produce a scanned aperture energly distribution and therefore a scanning far field pattern.

8. The invention set forth in claim 7 further defined in that said radiating elements each comprise a horn aperture directed to radiate substantially diametrically.

9. The invention set forth in claim 8 in which said horn apertures are essentially rectangular in shape and alternate ones of said columns of radiators around said circumference are shifted vertically thereby to permit interleaving of said horn apertures to facilitate closer effective circumferential radiating element spacing.

10. The invention set forth in claim 7 in which said columns of radiating elements are distributed over the full circumference of said cylindrical array.

References Cited UNITED STATES PATENTS 3,370,267 2/1968 Barry 343 X 3,394,380 7/1968 Pickles 343-854- RODNEY D. BENNETT, JR., Primary Examiner T. H. TUBBESING, Assistant Examiner US. Cl. X.R. 343-854 

